EXCHANGE 


The  Catalytic  Preparation 
of  Mercaptans 


DISSERTATION 

SUBMITTED  TO  THE  BOARD  OF  UNIVERSITY  STUDIES 

OF  THE  JOHNS  HOPKINS  UNIVERSITY  IN  PARTIAL 

FULFILMENT  OF  THE  REQUIREMENTS  FOR  THE 

DEGREE    OF    DOCTOR    OF    PHILOSOPHY 


BY 

RICHARD  L.  KRAMER 
BALTIMORE,  MD. 

February,  1920. 


EASTON,  PA. 

ESCHENBACH  PRINTING  COMPANY 
1921 


The  Catalytic  Preparation 
of  Mercaptans 


DISSERTATION 

SUBMITTED  TO  THE  BOARD  OF  UNIVERSITY  STUDIES 

OF  THE  JOHNS  HOPKINS  UNIVERSITY  IN  PARTIAL 

FULFILMENT  OF  THE  REQUIREMENTS  FOR  THE 

DEGREE    OF    DOCTOR    OF    PHILOSOPHY 


BY 

RICHARD  L.  KRAMER 
BALTIMORE,  MD. 

February,  1920. 

^ 


EASTON,  PA. 

ESCHENBACH  PRINTING  COMPANY 
1921 


' 

b 


EXCHANGE 


CONTENTS. 

1 .  Acknowledgment 4 

2.  Introduction 5 

3 .  Historical 5 

4 .  The  Apparatus 5 

5.  The  Method  of  Work 6 

6 .  The  Product 6 

7 .  The  Catalyst 7 

8.  Regereration  of  Catalyst 9 

9 .  A  Study  of  the  Reaction 9 

I  Effect  of  Temperature 9 

II  Rate  of  Flow 10 

III  Ratio  of  Reactants 11 

10 .  Comparison  of  Alcohols 11 

11 .  Purification  of  Product 11 

12.  Comparison  with  Sabatier's  Results 14 

13 .  Summary 14 

14 .  Biography 16 


544007 


ACKNOWLEDGMENT. 

The  author  wishes  to  express  his  appreciation  of  the  interest  shown 
and  assistance  given  by  Professor  E.  Emmet  Reid,  under  whose  direc- 
tion this  investigation  was  carried  out. 

He  also  takes  this  opportunity  to  express  his  appreciation  for  the  aid, 
instruction  and  encouragement  received  from  Professors  Frazer,  Pat- 
rick, Lovelace  and  Ames. 


THE  CATALYTIC  PREPARATION  OF  MERCAPTANS. 


Introduction. 

The  problem  of  the  preparation  of  alkyl  mercaptans,  especially  w-butyl 
mercaptan,  was  assigned  to  this  laboratory  in  connection  with  inves- 
tigations carried  out  in  the  war  work.  A  survey  of  the  methods  in  the 
literature  excited  interest  in  a  catalytic  process  which  appeared  to  pos- 
sess exceptional  possibilities  for  development.  Accordingly  an  investiga- 
tion of  it  was  made  which  resulted  in  the  erection  of  a  small  plant  for 
the  production  of  butyl  mercaptan  which  will  be  described  in  a  separate 
article.1  Later,  after  the  war,  the  problem  was  more  thoroughly  inves- 
tigated to  clear  up  a  number  of  difficulties  which  arose  in  the  operation 
of  the  process  and  for  its  general  scientific  interest. 

Historical. 

Sabatier2  discovered  the  catalytic  method  in  his  work  with  metallic 
oxides  as  dehydrating  catalysts  in  organic  reactions.  The  method  as  de- 
scribed consists  in  passing  a  mixture  of  alcohol  vapor  and  hydrogen  sul- 
fide  over  thoria  heated  to  300-380°,  the  resulting  product  being  a  mixture 
of  mercaptan,  unchanged  alcohol  and  some  sulfide.  A  portion  of  the 
alcohol  is  converted  into  the  olefine  hydrocarbon,  which  in  the  case  of 
secondary  alcohols  is  quite  large.  The  mercaptan  was  separated  and 
purified  by  fractional  distillation.3  In  a  later  communication,4  Sabatier 
compared  the  activities  of  a  number  of  metallic  oxides  by  means  of  iso- 
amyl  alcohol  at  370-384°,  and  found  thoria  to  be  the  best  catalyst,  credit- 
ing it  with  a  70%  yield  of  fs0-amyl  mercaptan. 

The  description  of  the  method  does  not  include  information  as  to  the 
rate  at  which  the  mixture  of  alcohol  and  hydrogen  sulfide  was  passed  over 
the  catalyst,  the  proportions  of  each  in  the  mixture,  or  the  amount  of 
thoria  used,  though  it  may  be  inferred  that  the  apparatus,  quantities  of 
materials  and  rates  of  passage  were  analogous  to  those  used  in  his  study  of 
the  dehydration  of  alcohols.5 

Apparatus. 

The  catalyst  was  contained  in  a  hard  glass  tube  20  X  640  mm.,  which 
was  uniformly  heated  in  a  special  horizontal  electric-tube  furnace  auto- 

1  In  this  investigation  Dr.  J.  W.  Kimball,  Mr.  George  Holm,  Mr.  G.  W.  Livingston 
and  Mr.  R.  W.  Hale,  Jr.,  also  took  part.     Though  their  results  are  not  included  in  the 
present  article,  credit  is  due  them  for  assistance  in  laying  the  foundation  for  the  present 
work. 

2  Sabatier,  Compt.  rend.,  150,  1217  (1910). 

3  See  section  on  distillation  of  mixtures  of  mercaptan  and  alcohol, 

4  Sabatier,  Compt.  rend.,  150,  1569  (1910). 

5  Ibid.,  146,  1377  (1908). 


,» 
6 


matically  regulated  to  about  1°.  The  temperature  was  read  on  a  ther- 
mometer placed  between  the  catalyst  tube  and  the  wall  of  the  furnace. 
Tests  showed  that  this  registered  about  20°  above  the  temperature  inside 
the  catalyst  tube,  hence  the  temperatures  given  in  tables  are  20°  lower 
than  those  actually  read. 

The  hydrogen  sulfide  was  generated  in  a  Kipp  apparatus  and  was  washed 
with  water,  dried  over  calcium  chloride  and  measured  by  a  calibrated 
flowmeter.  It  averaged  95%  pure. 

The  alcohol  was  admitted  from  a  dropping  funnel  with  a  calibrated  tip 
to  a  tube  reaching  to  the  bottom  of  a  distilling  bulb  through  which  the 
hydrogen  sulfide  was  passed.  This  bulb  was  immersed  in  an  oil-bath 
and  served  as  a  flash-boiler  to  vaporize  the  alcohol  and  as  a  mixing  cham- 
ber for  the  vapor  and  the  gas,  the  mixture  being  led  directly  into  the 
furnace.  The  reaction  products  passed  through  a  condenser  cooled  with 
ice-water  into  a  receiver  packed  in  ice.  The  uncondensed  portion  was 
led  through  caustic  alkali  solution  and  the  remaining  gas  collected  over 
water  in  a  large  calibrated  aspirator  bottle. 

Method  of  Work. 

While  the  furnace  was  heating,  the  rates  of  flow  of  hydrogen  sulfide 
and  alcohol  vapor  were  adjusted,  the  products,  being  run  out  through 
a  3-way  cock  placed  between  the  condenser  and  receiver.  When  the 
desired  conditions  were  attained  one  gram  molecule  of  the  alcohol  was 
placed  in  the  dropping  funnel,  the  stopcock  turned  so  as  to  connect  with 
the  receiver  and  the  time  taken.  As  the  last  of  the  alcohol  ran  in,  the 
receiver  was  disconnected  and  the  time  taken  again. 

The  Product. 

The  condensate  usually  consisted  of  2  layers;  the  lower,  or  water  layer, 
was  discarded  and  the  other  weighed  and  entered  as  "product."  The 
upper  layer  in  the  receiver,  except  in  the  case  of  the  methyl  compound, 
which  demanded  special  treatment,  consisted  of  mercaptan,  unchanged 
alcohol,  aldehyde,  ether,  water  and  condensation  products  saturated  with 
hydrogen  sulfide  and  unsaturated  hydrocarbon. 

The  liquid  was  freed  from  hydrogen  sulfide  by  boiling  under  a  well- 
cooled  reflux  condenser  for  20  minutes,  or  until  a  test  portion  showed  no 
hydrogen  sulfide  with  alcoholic  lead-acetate  solution.  The  mercaptan 
present  was  then  determined  iodometrically.1  The  gaseous  products  col- 
lected consisted  of  the  unsaturated  hydrocarbon  resulting  from  dehydra- 
tion of  a  part  of  the  alcohol,  hydrogen  corresponding  to  the  aldehyde  pro- 
duced and  hydrogen  originally  present  as  impurity  in  the  hydrogen  sul- 
fide, together  with  a  small  amount  of  air  from  the  receiver.  A  measured 
sample  was  shaken  with  bromine  water  to  determine  the  unsaturated 
1  Kimball,  Kramer  and  Reid,  /.  Am.  Chem.  Soc.  43,  1199  (1921). 


hydrocarbon.     The  analysis  of  the  residue  from  an  average  run  showed 
it  to  be  nearly  pure  hydrogen. 

Methyl  mercaptan  boiling  at  6°  required  special  treatment.  It  was 
absorbed  in  the  caustic  soda  wash-bottles,  the  resultant  alkaline  solution 
placed  in  a  flask,  the  exit  tube  of  which  was  connected  with  a  coil  con- 
denser surrounded  with  freezing  mixture,  and  the  mercaptan  was  dis- 
placed by  passing  hydrogen  sulfide  into  the  solution.  No  hydrogen  sul- 
fide  passed  through  till  all  of  the  mercaptan  had  been  displaced.  The 
mercaptan  was  collected  in  well-cooled  tared  tubes  which  were  sealed  and 
weighed. 

The  Catalyst. 

Thoria  has  been  used  as  a  catalyst  throughout  the  work;  much  time 
has  been  spent  studying  different  methods  of  its  preparation  so  as  to 
obtain  maximum  activity.  Comparing  this  oxide  with  alumina  and  others 
the  activity  of  which  is  greatly  influenced  by  mode  of  preparation, l  Saba- 
tier  says,2  "On  the  contrary  thoria  does  not  present  this  inconvenience 
and  its  activity  is  not  sensibly  diminished  when  it  is  ignited  at  a  red 
heat;  it  seems  that  so  heavy  a  molecule  can  not  undergo  further  important 
molecular  condensations." 

Our  experiments  show  that  the  mode  of  preparation  of  thoria  greatly 
influences  its  activity  in  this  reaction,  some  preparations  being  absolutely 
inactive. 

Commercial  thoria  and  discs  cut  from  Welsbach  gas  mantles  were 
found  to  be  inactive.  When  thorium  nitrate  is  heated  suddenly  to  a 
high  temperature  by  being  dropped  into  a  red  hot  crucible  a  very  light 
porous  thoria  is  obtained,  7  g.  of  it  occupying  200  cc.  of  space.  On  ac- 
count of  its  enormous  surface  we  expected  this  to  be  a  wonderfully  active 
form  but  found  it  inactive.  A  thoria  gel  prepared  according  to  Miiller* 
was  found  to  be  inactive  alone  but  when  the  concentrated  hydrosol  was 
distributed  on  pumice,  Catalyst  E,  before  the  final  evaporation  a  fair 
catalyst  was  obtained.  The  precipitated  and  carefully  washed  hydroxide 
from  44  g.  of  pure  thorium  nitrate  was  suspended  in  300  cc.  of  pure  water, 
which  was  rapidly  stirred  at  90°  while  4  g.  of  thorium  nitrate  in  20  cc. 
of  water  was  added.  The  hydroxide  dissolved  to  form  an  orange-yellow 
hydrosol.  The  volume  was  reduced  to  20  cc.  on  the  water-bath  and  the 
hydrosol  evaporated  in  a  vacuum  desiccator  to  a  hard  glass-brittle  light 
green  solid.  This  was  dehydrated  at  400  °  in  a  current  of  air. 

On  account  of  the  high  cost  of  thoria,  its  density,  and  tendency  to  pack, 
a  number  of  experiments  were  made  with  different  proportions  of  thoria 
on  pumice  as  a  carrier. 

1  Sabatier,  Compt.  rend.,  147,  106  (1909). 

2  Sabatier,  "La  Catalyse,"  2nd  Ed.,  Paris,  1920,  p.  26. 

3  Mueller,  Ber.,  39,  2857  (1906). 


8 

The  best  catalyst  obtained  was  prepared  as  follows.  Pumice  sized 
between  6-  and  12-mesh  sieves  was  placed  in  a  dish  on  a  water-bath  and 
a  cone,  water  solution  of  analyzed  thorium  nitrate  poured  over  it,  the 
quantities  being  so  taken  that  the  ratio  of  pumice  to  thoria  should  be  3: 1. 
Other  ratios  were  tried  but  gave  poorer  results.  The  mass  was  contin- 
ually turned  during  the  evaporation  of  the  water.  The  material  may  be 
further  dried  in  an  oven  at  120°.  This  was  done  with  Catalyst  F  while 
G  and  H  were  not  so  dried.  Catalyst  F  was  easily  duplicated  and  proved 
to  be  reliable  and  efficient;  it  was  used  in  all  of  our  subsequent  work. 
The  thorium-nitrate — pumice  was  placed  in  a  tube  in  a  current  of  air 
and  heated  to  270°,  the  decomposition  temperature  of  the  nitrate,  till 
decomposition  was  nearly  complete,  after  which  the  temperature  was 
gradually  raised  to  400°,  and  air  passed  until  the  issuing  gas  would  no 
longer  redden  moist  litmus.  A  snow-like  coating  of  thoria  covered  the 
pumice. 

C  and  D  were  preliminary  catalysts  prepared  in  this  way  except  that 
the  proportion  of  thoria  and  the  decomposition  temperatures  varied. 

Catalyst  A  was  prepared  by  igniting  precipitated  thorium  hydroxide 
which  had  been  carefully  washed  to  remove  electrolytes.  It  was  mixed 
with  glass  wool  to  keep  it  suspended. 

The  table  below  gives  the  results  with  various  catalysts,  74  g.  of  n- 
butyl  alcohol  with  an  equivalent  amount  of  hydrogen  sulfide  being  passed 
over  the  catalyst  at  380  °  in  6  hours  except  with  Catalysts  E  and  H ,  where 
it  was  4  hours. 

TABLE  I.— COMPARISON  OP  CATALYSTS. 

Thoria.  Pumice.  Temp,  of  prep.  Yield. 

Expt.  Catalyst.  G.  G.  °  C.  %. 

1  A  20  none  Below  red  35 . 8 

2  B  19  37.5  Below  red  43.5 

3  C  6  44  400  34.4 

4  C  6  44  450  26.6 

5  C  6  44  550  21.1 

6  D  12.5  37.5  400  44.4 

7  D  12.5  37.5  500  42.7 

8  E  25  X  ...  38.8 

9  F  12.5  37.5  270-400  50.2 

10  F  12.5  37.5  270-400  52.1 

11  F  12.5  37.5  270400  52.7 

12  G                     8  42  270-400  44.0 

13  G  8  42  270-400  45.7 

14  H  12.5  37.5  270-400  49.9 

15  H  12.5  37.5  270-400  50.1 

From  these  figures  it  appears  that  a  given  weight  of  thoria  is  considerably 
more  effective  if  distributed  on  a  carrier.  From  Expts.  3,  4,  5,  and  6-7, 
it  appears  that  the  activity  of  the  thoria  is  considerably  diminished  by 
heating  much  above  400°.  Catalyst  H  is  the  most  efficient. 


9 

Regeneration  of  Catalyst. 

The  catalyst  becomes  coated  slowly  at  380°,  and  more  rapidly  at  higher 
temperatures,  with  carbonaceous  material  and  its  activity  diminishes.  A 
fouled  catalyst  may  be  cleaned  by  passing  steam  through  it  at  380°  until 
all  volatile  material  is  removed  and  following  this  with  nitrogen  peroxide 
at  the  same  temperature  as  long  as  there  is  any  action.  The  oxides  of 
nitrogen  are  then  completely  displaced  with  steam.  The  regenerated 
catalyst  is  snow-white  and  shows  its  original  activity. 

Effect  of  Temperature. 

One  gram  mol  of  n-butyl  alcohol  was  passed  with  an  equivalent  amount 
of  hydrogen  sulfide  over  Catalyst  F  in  6  hours,  the  product  weighed,  and 
the  mercaptan  determined.  For  the  higher  temperatures  the  butylene 
was  determined  and  the  aldehyde  estimated  from  the  amount  of  hydrogen 
remaining,  allowing  for  the  hydrogen  present  in  the  hydrogen  sulfide,  the 
alcohol  being  taken  by  difference.  Some  butyl  sulfide  was  doubtless 
formed  but  it  was  not  taken  into  account  as  the  amount  is  relatively 
small  and  no  convenient  method  of  estimating  it  is  known.  The  results 
are  given  in  Table  II  below  and  in  Fig.  1  the  yields  are  plotted  against 
temperature.  In  order  to  show  the  effect  of  the  catalyst  on  the  alcohol 
alone  the  last  three  runs  were  made  without  the  hydrogen  sulfide,  under 
the  same  conditions. 

TABLE  II. — EFFECT  OP  TEMPERATURE. 

Product.  Alcohol  converted. 

. .  . • .  Alcohol 

Temp.         Weight.             Analysis.  BuSH.             C4H8.            PrCHO.  by  dif. 

Expt.             °C.                G.                        %.                     %.                   %.                   %.  %. 

1  260  75  9.3              7.7 

2  280  78  14.3  12.4 

3  300  82  21.7  19.7 

4  320  84  29.3  27.4 

5  340  80.5  38.2  34.2            0.3              5.1            60.4 

6  360  82.5  47.3  43.4             1.2            10.0            45.4 

7  360  78.5  48.5  42.3             1.7            11.3            44.7 

8  380  77  59.6  50.2 

9  380  76.5  61.3  52.1            1.8            15.1            31.0 

10  380  73.5  64.6  52.7  2.1  17.4  27.8 

Alcohol  alone. 

11  340             •       0.5  7.7  91.8 

12  360             ....              ....             ....  2.1  17.7  80.2 

13  380            ....             ....             ....  2.7  32.7  64.6 

From  these  results  it  appears  that  the  yield  of  mercaptan  increase  regu- 
larly with  the  temperature  but  on  account  of  the  increasing  prominence 
of  side  reaction  it  is  not  advisable  to  go  above  380°.  Fouling  of  the 
catalyst  interferes  above  this  temperature. 

The  rate  of  formation  of  butylene  is  surprisingly  low,  and  is  not  serious 
even  at  380°;  that  is,  this  catalyst  appears  to  be  more  active  in  the  de- 


10 


32<T  U 

Jemperoture 

Fig.  1. 


hydrogenation  than  in  the  dehydration  of  butyl  alcohol.  This  is  sur- 
prising in  view  of  Sabatier's1  statement  that  thoria  is  exclusively  a  de- 
hydrating catalyst  for  alcohols. 
At  380°  52%  of  the  alcohol  is 
converted  into  mercaptan  and 
33%  of  the  remaining  48%  into 
aldehyde,  while  in  the  run  with 
alcohol  alone  32.7%  of  aide-  *, 
hyde  formation  was  observed.  | 
At  lower  temperatures  some- 
what the  same  relations  hold, 
indicating  that  the  aldehyde 
formation  depends  on  the  re- 
maining alcohol  rather  than  on  that  originally  present.  Less  butylene  is 
formed  when  hydrogen  sulfide  is  present,  though  the  difference  is  not  great. 

Rate  of  Flow. 

The  influence  of  rate  of  passage  of  the  vapor  mixture  over  the  catalyst 
was  investigated  by  making  a  series  of  runs  at  380°  using  74  g.  of  butyl 

alcohol  for  each  run, 
and  hydrogen  sulfide  in 
equivalent  amounts. 
The  results  are  given  in 
Table  III  and  plotted 
in  Fig.  2.  The  yield 
of  mercaptan  increases 
with  the  time  until  the 
rate  of  6  hours  for  1 
gram  mole  is  reached. 

rime  in  Hours  por  the  amount  of  cat- 

Fig-  2'  alyst  used,  this  is  the 

TABLE  III. — INFLUENCE  OF  RATE  OF  FLOW  OF  VAPOR  MIXTURE. 


to 
so 

r 

r 

*„• 

to 

^< 

^ 

^ 

> 

S 

^ 

/ 

1           Z           3          4           S           6           7           8           9          10          II         12 

Expt. 

1 

2 

3 

4 

5 

6 

7 

8 

9 
10 
11 


Time. 
Hours. 

1 

2 

3 

3 

4 

5 

6 

6.3 

7.1 

8.5 

12 


Alcohol  converted. 


72.5 
79.0 
78.0 
78.5 
77.5 
76.0 
77.0 
76.5 
73.5 
76.0 
68.0 


29.9 
35.1 
43.1 
43.0 
46.9 
54.0 
59.6 
61.3 
64.6 
61.3 
71.4 


BuSH. 

C<H«. 

PrCHO. 

22.4 

0°3 

3°4 

30.8 

0.5 

7.4 

37.3 

0.5 

10.5 

37.5 

0.8 

8.7 

40.4 

1.0 

11.0 

45.6 

1.4 

13.1 

50.2 

. 



52.1 

1.8 

15.1 

52.7 

2.1 

17.4 

51.8 

1.4 

17.6 

53.8 

2.0 

23.2 

Remaining 
by  dif. 

%. 

73.9 
61  .'3 
51.7 
53.0 
47.6 
39.9 

31.0 

27.8 
29.2 
21.0 


Sabatier,  "La  Catalyse,"  2nd  Ed.,  Paris,  1920,  p.  261. 


11 


60% 


50% 


best  rate.     Doubling  the  time  results  in  a  very  slight  increase  in  the 
amount  of  mercaptan  with  a  considerable  increase  in  the  by-products. 

Ratio  of  Reactants. 

A  brief  study  was  made  of  the  ratio  of  the  reactants.     The  hydrogen 
sulfide  which  passes  out  of  the  reaction  tube  mixed  with  hydrogen  and 

hydrocarbon  is  a  loss  and  the 
greater  its  volume  the  more  of 
the  mercaptan  it  carries  along 
with  it.  On  the  other  hand, 
the  amount  of  alcohol  lost  in 
side  reactions  is  greater  when  it 
is  in  excess.  A  series  of  deter- 
minations was  made  at  380° 
passing  74  g.  of  n-butyl  alcohol 
over  the  catalyst  mixed  with 
varying  amounts  of  hydrogen 
sulfide.  The  results  are  given 
The  1 : 1  ratio  gives  the  best  results. 


401 


2CI 


0  O.I 

Lo<j  ratio  BuOH:H2S 

Fig.  3. 


in  Table  IV  and  plotted  in  Fig.  3. 


IV. — EFFECT  OF  CHANGE  OF  RATIO  OF  REACTANTS. 


Product. 


Alcohol  converted. 


Expt. 

H2S  :  BuOH. 

Weight. 
G. 

Analysis. 
%. 

1 

2        :  1 

74 

43.4 

2 

1.5    :  1 

76 

54.0 

3 

1        :  1 

76.5 

61.3 

4 

0.75  :  1 

73.5 

63.3 

BuSH. 

C4H8. 

PrCHO. 

35°  6 

0°7 

15°  8 

45.6 

1.2 

11.3 

52.1 

1.8 

15.1 

52.7 

1.0 

12.1 

Remaining 
by  dif. 

47°.  8 

41.9 
31.0 
33.3 

Comparison  of  Alcohols. 

A  brief  study  was  made  of  other  alcohols  under  the  conditions  that 
had  been  found  best  for  butyl  alcohol,  namely,  passing  one  mole  of  the 
alcohol  vapor  mixed  with  an  equivalent  amount  of  hydrogen  sulfide  in 
6  hours  over  Catalyst  F  at  380°,  except  for  methyl  and  ethyl  alcohols 
which  were  run  at  several  temperatures.  The  alcohols  were  anhydrous 
except  as  noted  for  one  run  with  ethyl  alcohol.  The  results  are  given  in 
Table  V. 

At  380°  methyl  and  ethyl  alcohols  give  about  the  same  results,  the 
yield  increasing  with  propyl  and  still  more  with  n-butyl  alcohol.  The 
*s0-alcohols  give  somewhat  lower  yields  but  better  with  the  larger  molec- 
ular weight.  These  two  alcohols  give  notably  less  aldehyde  than  the 
others. 

Methyl  alcohol  gives  a  somewhat  better  yield  at  370°  than  at  380°. 
Purification  of  Product. 

The  purification  of  the  crude  product  from  the  furnace  varies  con- 
siderably with  the  alcohol  used.  A  method  of  recovering  and  purifying 
methyl  mercaptan  has  already  been  outlined.  In  the  case  of  ethyl  and 


12 

propyl  mercaptans  advantage  is  taken  of  the  fact  that  the  alcohols  are 
extremely  soluble  in  water  and  can  be  washed  out  of  the  crude  material. 
After  washing  with  water  the  residue  consisting  of  mercaptan,  sulfide  and 
other  products  is  treated  with  alkali  to  dissolve  the  mercaptan  and  sep- 
arated. The  addition  of  mineral  acid  to  the  alkaline  solution  frees  the 
mercaptan  which  is  washed,  dried  and  fractioned. 

TABLE  V. — COMPARISON  OF  ALCOHOLS. 

Product.  Alcohol  converted. 


Temp. 

Weight. 

Analysis. 

RSH. 

C«H2w. 

RCHO. 

CWUUUUUIM 

by  dif. 

Expt. 

Alcohol. 

°c. 

G. 

%• 

%. 

%. 

%. 

%• 

1 

Methyl 

370 

20 

100 

41.6 

.... 

14.3 

44.1 

2 

Methyl 

380 

17.3 

100 

36.0 



15.9 

49.1 

3 

Ethyl 

350 

35 

49.4 

27.8 

4 

Ethyl 

360 

32 

66.3 

35.4 

5 

Ethyl 

360 

31 

68.0 

35.0 

g 

Ethyl 

370 

28 

77.4 

34.9 

7 

Ethyl  95% 

365 

29 

67.1 

32.4 

7.16 

11.0 

49.4 

8 

Propyl 

380 

60 

56.7 

44.7 

0.6 

14.1 

40.2 

9 

Propyl 

380 

61 

56.1 

45.1 

0.7 

13.2 

41.0 

10 

n-Butyl 

380 

76.5 

61.3 

52.1 

1.8 

15.1 

31.0 

11 

*'s0-Butyl 

380 

72 

44.6 

35.7 

3.0 

7.2 

54.1 

12 

iso-Amyl 

380 

92 

47.3 

41.8 

2.8 

9.5 

45.9 

13 

iso-Amyl 

380 

94 

47.4 

41.8 

2.8 

6.7 

47.7 

The  higher  alcohols  are  difficultly  soluble  in  water,  but  an  alkali  sep- 
aration cannot  be  used  because  the  alcohol  dissolves  in  an  alkaline  solu- 
tion containing  mercaptan.  Eor  example,  100  g.  of  water  dissolves  but 
8.3  g.  of  w-butyl  alcohol ;  but  a  mixture  of  the  alcohol  and  mercaptan  where 
the  latter  is  present  to  the  extent  of  50%  or  better  is  completely  soluble 
in  a  20%  solution  of  sodium  hydroxide. 

The  alcohols  can  not  be  separated  from  the  higher  mercaptans  by 
distillation  because  they  form  constant-boiling  mixtures  boiling  only  at 
slightly  lower  temperatures  than  do  the  mercaptans.  When  a  simple 
distilling  apparatus  is  used  this  is  not  evident  except  by  analysis  of  the 
fraction  corresponding  to  the  pure  mercaptan.  Having  observed  this 
fact  first  in  connection  with  w-butyl  mercaptan  an  investigation  was  also 
made  of  propyl  and  iso-amyl  mercaptans  to  determine  accurately  these 
mixtures  and  their  compositions.  As  Sabatier  had  separated  his  product 
by  fractional  distillation  it  was  expected  that  this  information  would  throw 
some  light  on  the  wide  variations  in  yield  which  he  reported  from  those 
obtained  in  this  work. 

The  method  employed  consisted  in  distilling  the  constant  boiling  mix- 
ture from  a  sample  of  equal  parts  o"F  alcohol  and  mercaptan.1  The  frac- 
1  Note:  It  is  very  difficult  to  approach  the  constant-boiling  mixture  from  the 
other  side  because  of  the  slight  difference  in  boiling  points  of  the  mixture  and  the 
mercaptan. 


13 

tion  collected  was  analyzed  and  redistilled  to  check  the  first  determina- 
tion. When  the  customary  fractionating  columns  were  used  the  varia- 
tion in  the  analyses  of  these  fractions  was  large,  becoming  constant  only 
after  a  considerable  number  of  distillations.  Therefore  to  make  the  sep- 
aration as  complete  as  possible  a  Dufton1  column  was  used  because  of 
its  high  efficiency.  As  mercaptans  attack  metal  it  was  necessary  to  con- 
struct the  column  entirely  of  glass.  An  example  will  illustrate  the  method. 
A  mixture  of  equal  parts  of  w-butyl  alcohol  and  mercaptan  was  distilled 
and  the  first  fraction  from  97.6°  to  98.0°  collected  which  distilled  con- 
stantly at  97.8°.  This  fraction  analyzed  84.49%  mercaptan.  On  re- 
distillation it  gave  at  the  same  temperature  a  distillate  which  was  col- 
lected in  three  parts.  The  first,  middle  and  last  portion  analyzed  respec- 
tively 85.13%,  85.11%,  85.25%  mercaptan.  The  results  obtained  for 
the  mixtures  of  w-propyl,  w-butyl  and  is0-amyl  mercaptan  and  alcohol  on 
distillation  are  recorded  below,  together  with  the  boiling  points  of  the 
components. 

B.  p.  of  constituents.  Composition. 

°C.  %. 

w-Propyl  alcohol 97.4  8.65 

w-Propyl  mercaptan 67-68  91 . 35 

Constant  boiling  mixture 66 . 4  at  765 . 6  mm. 

w-Butyl  alcohol 117.02  14.84 

n-Butyl  mercaptan 97-98  at  753  mm.  85. 16 

Constant  boiling  mixture 97 . 8  at  770 . 3  mm. 

iso- Amyl  alcohol 131  22.89 

t'so-Amyl  mercaptan 116  77. 11 

Constant  boiling  mixture 115.6  at  766.9  mm. 

The  compositions  of  the  constant-boiling  mixtures  represent  the  limits 
of  separation  for  mixtures  of  mercaptan  and  alcohol. 

A  better  separation  of  these  mixtures  can  be  made  by  distilling  with 
steam,  but  only  in  the  case  of  propyl  mercaptan  is  the  separation  suffi- 
ciently complete  to  be  of  any  practical  value.  To  determine  the  effect 
of  distilling  with  steam,  water  was  added  to  the  mixture  of  alcohol  and 
mercaptan.  This  insures  good  contact  between  the  steam  and  mixture 
layer  reducing  the  amount  of  water  distilling  to  a  minimum.  The  dis- 
tillation was  carried  out  as  described  above.  The  table  gives  the  boiling 
point  of  the  ternary  vapor  mixture  and  the  analysis  of  the  mercaptan- 
alcohol  layer  in  the  distillate. 

TERNARY  MIXTURES. 
Mercaptan,  alcohol  and  water. 

Mercaptan 

B.  p.  Pressure.  in  upper  layer. 

0  C.  +yim.  %. 

w-Propyl 60.8  771.6  96.00 

w-Butyl 78.6  761.0  93.16 

iso-Amyl 86.6  765.4  88.85 

i  J.  Soc.  Chem.  2nd.,  38,  45T  (1919). 


14 

According  to  Claison  and  others  mercaptans  can  be  prepared  practi- 
cally pure  from  a  heavy  metal  salt.  The  lead  salt  is  the  one  usually  em- 
ployed. It  is  precipitated  in  an  alcoholic  water  solution,  filtered  and 
washed  several  times  with  alcohol.  After  drying  to  remove  the  alcohol 
the  mercaptan  is  recovered  by  distilling  the  salt  with  dilute  mineral  acid. 
This  method  yields  mercaptans  which  analyze  better  than  98.5%. 

The  lead  salt  of  n-butyl  mercaptan  precipitated  as  described  above  is 
a  yellow  crystalline  solid  which  melts  at  about  80°  to  an  orange-red  vis- 
cous liquid.  This  liquid  is  but  very  slowly  hydrolyzed  when  boiled  with 
water.  This  fact  led  to  the  following  method  for  the  preparation  of  pure 
butyl  mercaptan.  A  crude  sample  was  precipitated  in  alcoholic  solution 
with  lead  acetate  and  filtered.  The  salt  was  transferred  to  a  flask,  warmed 
to  100°  in  an  oil-bath  and  steam  passed  through  the  liquid  to  remove  the 
volatile  materials.  Due  to  hydrolysis  the  condensate  will  always  con- 
tain some  mercaptan  but  when  this  becomes  very  small  the  steam  is  shut 
off.  Dil.  mineral  acid  was  added  in  small  portions  at  a  time  and  the 
mercaptan  driven  over  with  steam.  It  was  separated  from  the  water, 
dried  over  anhydrous  sodium  carbonate  and  distilled.  It  came  over  in 
a  fraction  between  98°  and  98.2°  at  766.3  mm.,  the  temperature  remain- 
ing practically  constant  during  the  distillation  at  the  higher  temperature. 
An  analysis  of  this  sample  gave  the  results  99.28  and  99.39%. 

Comparison  with  Sabatier's  Results. 

It  is  difficult  to  compare  the  results  obtained  in  this  work  with  those 
of  Sabatier  because  he  gives  a  yield  for  but  one  alcohol.  In  comparing 
the  activity  of  various  oxides  as  catalysts  for  the  reaction  he  stated  that 
iso-amyl  alcohol  gave  with  thoria  at  370°  to  384°  a  yield  of  70%.  The 
temperatures  agree  very  well,  but  the  wide  variations  in  yield  are  more 
difficult  to  explain.  This,  however,  is  probably  due  to  the  method  which 
he  used  to  separate  and  estimate  his  product,  namely,  fractional  distilla- 
tion. Assuming  that  he  used  a  very  good  column  for  his  separations  and 
that  he  obtained  the  constant  boiling  mixture  of  77.11%  mercaptan,  the 
actual  yield  would  then  have  been  but  54%.  If  he  used  only  one  of  the 
customary  columns  the  fraction  which  he  collected  boiling  at  116°  would 
unquestionably  have  had  a  much  lower  mercaptan  content  than  the 
constant-boiling  mixture,  as  has  been  found  from  experience.  With  these 
points  in  mind,  our  yield  of  47%  does  not  compare  so  unfavorably  with 
his  results.  A  specimen  of  *s0-amyl  mercaptan  purchased  before  the  war 
from  Kahlbaum  was  found  to  contain  71%  mercaptan. 

Summary. 

The  catalytic  preparation  of  mercaptan  has  been  studied.  By  passing 
alcohol  vapor  and  equivalent  hydrogen  sulfide  at  the  rate  of  one  mole  per 
hour  through  a  tube  containing  pumice  coated  with  12.5  g.  of  thoria  at 


15 


380°,  the  following  percentage  yields  of  mercaptans  were  obtained:  methyl 
41%,  ethyl  35%,  propyl  45%,  butyl  52%,  iso-butyl  45%,  wo-amyl  47%. 
Propyl,  butyl  and  iso-amy\  mercaptans  have  been  found  to  give  constant- 
boiling  mixtures  with  the  corresponding  alcohols  and  ternary  mixtures 
with  the  alcohols  and  water. 


BIOGRAPHY 

Richard  L.  Kramer  was  born  in  Frankfort,  Indiana,  in  1891,  where 
he  received  his  early  education.  He  was  graduated  from  the  Frankfort 
High  School  in  1909,  and  from  Wabash  College  (A.  B.)  in  1913.  During 
the  academic  years  of  1913-14,  1915-16  and  1916-17  he  was  a  graduate 
student  in  chemistry  at  Columbia  University.  He  entered  Johns  Hop- 
kins University  in  the  winter  of  1919. 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


AN  INITIAL  FINE  OF  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  5O  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


i     APT  27  1934 

MAY  28  1S45 

LD  21-100in  -7/33 

Photomount 
Pamphlet 

Binder 
Gaylord  Bros. 

Makers 
Syracuse,  N.  Y. 

PAT.  JAM  21,  1908 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


